Shift control system for continuously variable transmission

Abstract

A shift control system for a toroidal CVT employs a shift technique for setting a torque shift compensation quantity so as to be increased as an actual gear ratio approaches a low-speed side gear ratio region including a lowest-speed gear ratio and so as to be decreased when the actual gear ratio is in the low-speed side gear ratio region. Further, the shift control system is arranged to select a gear ratio in a low-speed side gear ratio region after a gear ratio in a high-speed side gear ratio region is selected.

What is claimed is:  
     
       1. A shift control system for a toroidal continuously variable transmission (toroidal CVT) of a vehicle, comprising: 
       a controller configured,  
       to calculate a command gear ratio of the toroidal CVT by adding a desired gear ratio and a torque shift compensation for compensating a difference between the desired gear ratio and an actual gear ratio which difference is generated by a shifting operation of the toroidal CVT,  
       to set the torque shift compensation quantity to increase as the actual gear ratio approaches a low-speed side gear ratio region including a lowest-speed gear ratio and to decrease when the actual gear ratio is the low-speed side gear ratio region.  
     
     
       2. The shift control system as claimed in  claim 1 , wherein the controller is further configured to prohibit to change the actual gear ratio from a gear ratio in a high-speed side gear ratio region to a gear ratio in the low-speed side gear ratio region after the actual gear ratio takes a gear ratio in the high-speed side gear ratio region except for the low-speed side gear ratio region. 
     
     
       3. The shift control system as claimed in  claim 2 , wherein the controller is further configured to prohibit to select the gear ratio in the low-speed side gear ratio region after the actual gear ratio takes the gear ratio in the high-speed side gear ratio region, even when the vehicle operates in a high load condition. 
     
     
       4. The shift control system as claimed in  claim 2 , wherein the controller is further configured to allow to select the gear ratio in the low-speed side gear ratio region when a vehicle speed is smaller than a low vehicle speed and when the vehicle is started. 
     
     
       5. The shift control system as claimed in  claim 4 , wherein the controller is further configured to select the lowest speed gear ratio when a vehicle speed is smaller than a first vehicle speed, and to select a low-side limit gear ratio, which smoothly varies between the low-speed side gear ratio region and the high-speed side gear ratio region, when the vehicle speed is in a range between the first vehicle speed and a second vehicle speed higher than the first vehicle speed. 
     
     
       6. The shift control system as claimed in  claim 1 , wherein the controller is further configured to limit a down shift due to a rapid deceleration of the vehicle to a predetermined gear ratio when the actual gear ratio is in the high-speed side gear ratio region and when the rapid deceleration is detected. 
     
     
       7. The shift control system as claimed in  claim 6 , wherein the controller is further configured to limit a down shift due to a rapid deceleration of the vehicle to a predetermined gear ratio within the high-speed side gear ratio region until one of first and second conditions is detected, the first condition including a condition that the rapid deceleration is terminated, and second condition includes a condition that the vehicle is reaccelerated. 
     
     
       8. The shift control system as claimed in  claim 6 , wherein the controller is further configured to prohibit to select the gear ratio in the low-speed side gear ratio region after the vehicle is reaccelerated. 
     
     
       9. A shift control system of a toroidal continuously variable transmission (toroidal CVT) for a vehicle, comprising: 
       a transmission rotation speed detector that detects an input rotation speed and the output rotation speed of the toroidal CVT;  
       an accelerator opening detector that detects a depression degree of an accelerator pedal;  
       a vehicle speed detector that detects a vehicle speed;  
       a shift control device that operates the toroidal CVT according to a command gear ratio;  
       a controller connected to the transmission rotation speed detector, the accelerator opening detector, a vehicle speed detector and the shift control device, the controller being configured,  
       to calculate an actual gear ratio of the toroidal CVT from the input and output rotation speeds of the toroidal CVT,  
       to calculate a desired gear ratio based on a shift map from the depression degree of the accelerator pedal and the vehicle speed,  
       to calculate the command gear ratio by adding the desired gear ratio and a torque shift compensation quantity for compensating a difference between the desired gear ratio and the actual gear ratio which difference is generated by a shifting operation of the toroidal CVT,  
       to set the torque shift compensation quantity so as to increase as the actual gear ratio approaches a low-speed side gear ratio region including a lowest-speed gear ratio and so as to decrease when the actual gear ratio is the low-speed side gear ratio region,  
       to prohibit to select a gear ratio in the low-speed side gear ratio region after the actual gear ratio takes a gear ratio in a high-speed side gear ratio region except for the low-speed region.  
     
     
       10. A shift control system for a toroidal continuously variable transmission (toroidal CVT) of a vehicle, comprising: 
       a command gear ratio calculating means for calculating a command gear ratio of the toroidal CVT by adding a desired gear ratio and a torque shift compensation for compensating a difference between the desired gear ratio and an actual gear ratio which difference is generated by a shifting operation of the toroidal CVT; and  
       a torque shift compensation quantity setting means for setting the torque shift compensation quantity so as to increase as the actual gear ratio approaches a low-speed side gear ratio region including a lowest-speed gear ratio and so as to decrease when the actual gear ratio is the low-speed region.  
     
     
       11. The shift control system as claimed in  claim 10 , further comprising a prohibiting means for prohibiting to change the actual gear ratio from a gear ratio in the high-speed side gear ratio region to a gear ratio in the low-speed side gear ratio region after the actual gear ratio is in the high-speed side gear ratio region except for the low-speed side gear ratio region. 
     
     
       12. The shift control system as claimed in  claim 11 , further comprising an allowing means for allowing to select the gear ratio in the low-speed side gear ratio region when a vehicle speed is smaller than a low vehicle speed. 
     
     
       13. The shift control system as claimed in  claim 12 , further comprising a lowest-speed gear ratio selecting means for selecting the lowest speed gear ratio when a vehicle speed is smaller than a first vehicle speed, and a low-side limit gear ratio selecting means for selecting a low-side limit gear ratio, which smoothly varies between the low-speed side gear ratio region and the high-speed side gear ratio region, when the vehicle speed is in a range between the first vehicle speed and a second vehicle speed higher than the first vehicle speed. 
     
     
       14. The shift control system as claimed in  claim 10 , further comprising a down-shift limiting means for limiting a down shift due to a rapid deceleration of the vehicle to a predetermined gear ratio when the actual gear ratio is in the high-speed side gear ratio region and when the rapid deceleration is detected.